1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to level shifter circuits for shifting data from one voltage domain to another.
2. Description of the Related Art
In many electronic devices, data must be conveyed from a first voltage domain (having a first power supply voltage) to a second voltage domain (having a second power supply voltage). Circuits used to accomplish this task are known as level shifters. A level shifter circuit is configured to receive data in the first voltage domain and output the data into the second voltage domain.
FIG. 1 is a schematic diagram of an exemplary level shifter. In the embodiment is shown, data from a first voltage domain having a supply voltage of 3.3 volts is input into the level shifter. Data is output from the level shifter into a voltage domain having a supply voltage of 1.6 volts. In general, level shifters may provide a downshift in voltage (as in the example here), or an upshift in voltage.
Level shifter circuits typically include a pair of cross-coupled inverter circuits that are coupled to an input circuit. In order to cause the transistors of the cross-coupled inverters to change states (when the data similarly changes states), the transistors of the input circuits must provide sufficient drive strength. Providing a sufficient amount of drive strength typically requires the implementation of an input circuit that utilizes devices capable of providing the drive strength necessary to change the state of the keeper circuit.